With growing evidence that boys, like girls, are maturing at ever younger ages, who’s ready with helpful advice?

Moms really can’t avoid having the puberty talk with their daughters — the arrival of their first periods makes sure of that. But now that boys — like girls — are hitting puberty earlier than ever, they’re going to need some sex ed too. The problem, according to at least one pediatrician, is that parents aren’t lining up to explain puberty to their sons. Moms feel awkward referencing penises, says Dr. Claire McCarthy of Boston Children’s Hospital, and dads aren’t socialized to tackle the topic. McCarthy, who discussed the subject on the hospital’s Thriving blog, says both moms and dads “look at me like I have three heads” when she recommends they talk about sex with their 10-year-olds. “Women have less comfort with it, and men have zero comfort,” she says. “That’s kind of a bad combination.”

For about 15 years, studies have been showing that girls are developing breasts and getting their periods earlier than they used to. And last month, researchers announced in the journal Pediatrics that the trend is true among U.S. boys as well. On average, the researchers found that African-American boys are experiencing the beginnings of genital growth, testicular enlargement and those first stray pubic hairs at 9.14 years old, compared with 10.14 years for white boys and 10.4 years for Hispanic boys. Boys are now maturing sexually up to two years earlier than boys did a few decades ago. The reason? The rising levels of childhood obesity are almost certainly to blame since hormones that regulate sexual development are stored in fat.

For parents, the trend means pushing up that dreaded discussion about sex. The conversations can be tricky to finesse, but they’re important. As hormone levels change, they result in more than just physical changes: they affect the brain as well, prompting tweens to start to have new and unexpected feelings of arousal. They may be confused, even angry. As puberty takes root, kids experiencing these changes at ever younger ages may be ill equipped to deal with their emotions. “It’s easier to talk from your experience, so it’s easier for women to talk to their daughters than to their sons because they didn’t have erections when a cute girl walked by,” says McCarthy. “Fathers can do this talk much better. But in every single family, the dads look kind of horrified when I talk about these things.”

Thomas Matlack, founder of the Good Men Project, bristles at the assessment that dads don’t talk about sex. “Men are much more interested in being active and involved fathers than they were 25 years ago, and that includes talking about sex,” says Matlack, who started the online magazine as a place for men to share thoughts about what it means to be a good husband, father and man. “We have to make boys feel comfortable in their own sexual skin. That means talking about everything.”

That goes for both dads and moms, despite the fact that McCarthy suspects many may be hesitating to talk about sex with their kids for fear of encouraging promiscuity. Some school-based sex-education curricula maintain an abstinence-only focus out of concern that teaching students about contraception will encourage them to become sexually active; some parents take the same approach, even though research from the Guttmacher Institute has proved that theory wrong.

“When it comes to sex, [parents] want to keep [their children] innocent,” says McCarthy. “They feel that if they have ‘the talk’ too early, it will make them more likely to have sex. Ninety percent of the time when I ask parents if they are talking with their kids about puberty around ages 9 or 10, they say no. Even when they get to be 16, they’re still not talking about it.” If the latest study trends are confirmed, at least parents can take solace in this: with puberty starting earlier and earlier, they can get the sex talk over with sooner.